The present invention relates in general to GPRS (General Packet Radio Service) and in particular to methods and systems for tunneling data packets whereby data packets could traverse either one of GSM (Global System for Mobile Communication) and a foreign network such as a TDMA (Time Division Multiple Access) network to reach a given MS (Mobile Station).
GPRS refers to a recently implemented high-speed packet data technology. GPRS is expected to profoundly alter and improve the end-user experience of mobile data computing, by making it possible and cost-effective to remain constantly connected, as well as to send and receive data at much higher speeds than in the past. Its main innovations are that it is packet based, that it can increase data transmission speeds from the previous 9.6 Kbps to over 480 Kbps, and that it may be used to extend the Internet connection all the way to the mobile PC. In other words, the user will no longer need to dial up a separate ISP. However, GPRS complements rather than replaces the prior art data services available through cellular networks, such as circuit-switched data and SMS (Short Message Service) that has been available in some cellular telephone networks such as GSM.
Because GPRS supports standard networking protocols, configuring computers to work with GPRS is very straightforward. In the case of IP communications, one is able to use existing TCP/IP protocol stacks, such as the stack that comes with widely available operating systems such as Windows 95. TCP/IP stacks are readily available for most other platforms as well.
Another feature of GPRS is that it supports a message transmission technology typically referred to as tunneling. Tunneling is the use of encapsulation to deliver messages through a network where that network has no knowledge of the message. One use of tunneling is to support private communications over a public network to provide what is known as a VPN (virtual private network). Software is used at each end of the communication to encapsulate sent and de-capsulate received messages. In accordance with the GPRS standard, traffic data packets are tunneled across any intervening networks from a SGSN (Serving GPRS Support Node) associated with a source of traffic data packets to a GGSN (Gateway GPRS Support Node) associated with the receipt of the traffic. To forward IP or X.25 packets between each other, the SGSN and GGSN encapsulate these packets using a specialized protocol called the GPRS tunnel protocol (GTP) which operates over the top of standard TCP/IP protocols.
The GPRS standard further defines three (3) classes of terminals or Mobile Stations. (MSs). A class A terminal may receive both switched circuit and packet data communications simultaneously. A class B terminal may be used in either a packet data mode or a switched circuit mode, but may not be used in both modes simultaneously. A class C terminal is only usable for packet data communications.
The GSM GPRS network, defined by ETSI standards beginning with 03.60, has been selected as the standard for use in the North American TDMA market for data packet service. Since GSM and TDMA use somewhat different approaches in providing signaling messages to and from a given MS there are some inconsistencies that need to be solved between the voice and data networks in the TDMA system. In other words, the standard TDMA method of delivering the signaling messages is not appropriate for an MS designed in accordance with the GSM GPRS packet data standard.
One possible solution for resolving the differences is to change the GPRS network to accept signaling information from the TDMA network. This approach is undesirable in that it would require a considerable amount of standards definition work. Further, if it came to pass that other networks wanted to be able to receive and transmit signaling messages to a MS designed in accordance with standards agreed upon in the in a GSM GPRS and North American TDMA (TDMA 136) GPRS, further standards definition work would be required. A more desirable approach is to find a method whereby a signaling path can be provided transparently through the GPRS network from any MSC (Mobile Switching Center) whether part of a GSM, TDMA-136, CDMA or other type cellular network, directly to any MS registered to that home MSC. If such a solution would allow a packet data MS to roam to and operate in foreign type networks, while still receiving signaling messages from its home network, the method would have great economic impact.
The present invention comprises a method of permitting a home MSC and an MS, registered with that home MSC, located anywhere in the GPRS network to exchange signaling messages through the process of assigning IP addresses to both the MSC and to the MS, when the MS registers with the GPRS network, tunneling encapsulated signaling messages through the network between the MS and its associated home MSC and de-encapsulating the signaling messages at the signaling message destination.